Facsimile dot printing system with stew correction

ABSTRACT

In a facsimile system a document is copied by a helical bar dot printer in which the helical bar has a plurality of convolutions. A plurality of hammer blades each spanning one convolution of the helical bar function to print dots in the pattern of the document. The document to be copied is scanned line by line by an optical scanner to produce signals to control the printer. The scan line of the scanner is divided into a plurality of segments which are scanned simultaneously to severally control simultaneous printing by the hammer blades. Means are provided independent of the optical scanner to control the printer to print selective alphanumeric characters. In one embodiment, the scan line and print line are skewed relative to the direction of movement of the document and the printing medium, respectively, to accommodate an alphanumeric code input to the printer.

United States Patent Potter Aug. 20, 1974 [54] FACSIMILE nor PRINTING SYSTEM WITH 3,599,227 8/1971 Cobb 346/74 ES STEW CORRECTION 3,622,70l 11/1971 Gardner 178/30 [76] Inventor: John T. Potter, 151 Sunnyside Blvd, Plainview, NY. 11803 [22] Filed: Apr. 23, 1971 [21] Appl. No.: 136,950

[52] US. Cl. 178/30, l78/6.6 R [51] Int. Cl. H041 21/00 [58] Field of Search 178/17 D, 17 R, 5, 5.4 ES,

l78/5.4 E, DIG. 27, 25, 30, 7.1, 6.6 R, 7.6

[56] References Cited UNITED STATES PATENTS 2,529,978 ll/l950 Thompson l78/6.6 R 2,618,702 11/1952 Thompson 178/7.1 E 2,619,533 11/1952 Ress 178/5 2,930,847 4/1960 Metzger 178/30 2,953,638 9/1960 Wintringham l78/7.6 X 3,174,427 4/1965 Taylor 178/30 3,233,037 2/1966 F011 178/5 3,286,029 11/1966 Simshauser et al. 178/30 3,324,240 6/1967 Kleinschmidt et a1. 178/25 3,409,904 11/1968 Maiershofer 346/101 3,512,158 5/1970 Scarbrough 178/30 3,524,022 8/1970 Schoenthal 178/15 III/ Primary Examiner-Thomas W. Brown Attorney, Agent, or Firm-Lane, Aitken, Dunner & Ziems [5 7 ABSTRACT In a facsimile system a document is copied by a helical bar dot printer in which the helical bar has a plurality of convolutions. A plurality of hammer blades each spanning one convolution of the helical bar function to print dots in the pattern of the document. The document to be copied is scanned line by line by an optical scanner to produce signals to control the printer. The scan line of the scanner is divided into a plurality of segments which are scanned simultaneously to severally control simultaneous printing by the hammer blades. Means are provided independent of the optical scanner to control the printer to print selective alphanumericcharacters. In one embodiment, the scan line and print line are skewed relative to the direction of movement of the document and the printing medium, respectively, to accommodate an alphanumeric code input to the printer.

6 Claims, 11 Drawing Figures OPTICAL SCANNER HAMMER HAMMER HAMMER HAMMER FIRING FIRING FIRING FIRING cIRcuIr QIRCUIT CIRCUIT cmcun' 2 1,

7 a zv n 27 "1C,..

ALPHA 1 NUMERIC a 1.. an PRINT I I CONTROL CIRCUIT J 33% mmmmzonu FIG. 5.

Fla; 4.

FIG. 6.

INVENTOR JOHN- T. POTTER BY 95W ATTORNEYS mmmmzomn INVENTOR JOHN T. POTTER MMQMV gQM ATT RNEYS meminmz m 3.830.975

FIG. 9.

FIG. l0.

c FREQUENCY COMPARATOR I45 1 I35 MOTOR :23 CONTROL Isl l I33 w, PHASE L0 W |39 PASS i COMPARATOR Fl LTER H d9 I47 l L INVENTOR upny'q T. POTTER ATTORNEYS 52 z 4 0m ZorEo zwl mvsmoa' 7 JOHN T POTTER l F ACSIMILE DOT PRINTING SYSTEM WITH STEW CORRECTION BACKGROUND OF THE INVENTION This invention relates to a facsimile copying system for copying documents, and more particularly, to an improved low-cost high-speed system of the type in which electrical signals are generated in response to the document to be copied by an optical scanner to control a helical bar dot printer to reproduce the document.

In related copying systems of the prior art, the document to be copied is scanned line by line serially and the document is reproduced as the document is scanned. These systems operate very slowly at about lines of print per minute. As a result, the use of such systems are limited to instances in which such slow re- SUMMARY OF THE INVENTION In accordance with the present invention, an optical scanner simultaneously scans a plurality of discreet segments of an incremental line on the document to be copied and produces signals in response to the pattern contained in the segments. These signals control the actuation of a plurality of blade hammers aligned in a row, each in position to strike a different convolution of a helical bar on a rotating drum. Each time a hammer is actuated, it prints a dot on a sheet on which the copying is taking place at the point where the hammer blade strikes the helical bar. The signal from each scanned segment controls the firing of a corresponding hammer to print a pattern of dots corresponding to the pattern existing in the scanned segment. After a line has been scanned on the document to be copied and the corresponding pattern of dots has been printed, the scanner scans the next adjacent incremental line on the document. The sheet on which the reproduction is taking place is advanced and the corresponding pattern of dots is printed in the next incremental line on the sheet. This process is continued until the entire document has been copied. Because several segments of an incremental line are scanned and copied simultaneously, the time required to copy the document is greatly reduced.

The optical scanner comprises two bars on which scanning photocells and scanning optics are mounted. The bars are reciprocated alternately to scan the document to be copied so that one bar can be returned to be in position to start scanning while the other bar is performing a scan of the document.

The blades of the helical bar printer are canted slightly so that the printer will print in a straight line even though the medium on which the printing is carried out is moving. To correspond with this feature, the document to be copied is moved continuously through the optical scanner and the bars of the optical scanner scan the document at the same angle that the blades of the printer are canted.

Another feature of the present invention enables code signals to be sent to the helical bar printer to cause the printer to print alphanumeric characters independently of the optical scanner. This feature enablesthe system of the present invention to copy a portion of a printed document, such as a heading, and to print any selected alphanumeric data on the same sheet supplied from another data source.

BRIEF DESCRIPTION or THE DRAWINGS FIG. 1 schematically illustrates the system of the present invention in block form.

FIG. 2 is a view in elevation schematically illustrating the optical scanner of the present invention.

FIG. 3 schematically illustrates the optical scanner of thepresent invention in section taken along the lines 33 of FIG. 2.

FIGS. 4, 5, and 6 are fragmentary views illustrating portions of the optical scanner in more detail.

FIG. 7 is a perspective view of a portion of the optical scanner illustrating how the scanning motion is provided in the scanner.

FIG. 8 is a graph illustrating the development of cams used in the optical scanner.

FIG. 9 illustrates one of the cams of the optical scanner.

FIG. 10 is a block diagram illustrating the system for synchronizing the scanner with the printer in the system of the present invention.

FIG. 11 schematically illustrates an alternative embodiment of the system shown in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in FIG. 1, the system of the present invention comprises in combination a helical bar printer designated generally by the reference number 11 and an optical scanner 13. The helical bar printer is disclosed in detail in copending application Ser. No. 39,404 of Henry P. Kilroy et al. filed May 21, 1970 now abandoned and assigned to the assignee of this application. The printer 11 comprises a drum 15 which is driven continuously at a high speed by a motor (not shown) in close proximity to a row of hammers 17 aligned along a line parallel to the axis of the drum 15. The printer has 12 hammers 17 although only four are shown in FIG. 1, for convenience of illustration. A helical bar 19 on the cylindrical surface of the drum 15 extends around the drum in one complete convolution for each hammer 17. Each hammer 17 comprises a blade 21 positioned so that the edge of the blade will strike the helical bar 19 when the hammer is actuated. Each blade 21 spans only one convolution of the helical bar 19 so that when the hammer is actuated, the blade will strike the bar 19 at only one point. Each of the hammers 17 comprises a light weight coil 23 fixed to each of the blades 21. Each coil is in a constant magnetic field provided by a permanent magnet field structure (not shown). The hammers 17 are each actuated by applying a firing pulse to the coil of the hammer, which in response to the applied firing pulse will drive the hammer blade 21 against the helical bar 19. Paper on which the printing is carried out and an ink or carbon ribbon (not shown) are positioned between the ham mer blades 21 and the drum 15 so that when a hammer is actuated and the hammer blade strikes the helical bar 19, a dot will be printed on the paper at the intersection of the blade and the helical bar.

As the drum rotates, the intersection between the helical bar 19 and each blade 21 will move repeatedly from left to right across the blade. As the intersection moves from left to right in one pass by a blade, the hammer can be actuated repeatedly to print a selected pattern of dots along a line corresponding to the edge of the hammer blade. This line extended along all of the blade edges is referred to as the print line. The paper on which the printing is carried out is moved through the print line as the printing is carried out so that lines of dot patterns can be printed contiguously on the paper.

As disclosed in the above-described copending application Ser. No. 39,404, the timing of the firing of the hammers can be controlled so that the printer prints patterns of dots in the form of alphanumeric characters. In the system of FIG. 1, the means to control the printing of dot patterns as alphanumeric characters is provided by the alphanumeric print control circuit 25, which applies pulses through OR gates 27 to hammer firing circuits 29. In response to each pulse received from an OR gate 27, each hammer firing circuit 29 will apply firing pulse to the corresponding hammer 17 and thus cause a dot to be printed. The alphanumeric print control circuit 25 in response to coded signals representing alphanumeric characters controls the timing of the pulses applied through the OR gates 27 to the hammer firing circuits 29 to print alphanumeric characters represented by the coded signals in the same manneras described in the above-mentioned copending application Ser. No. 39,404.

The optical scanner 13 will scan a document to be copied and produce signals on channels 31 indicating whether the scanned portions of the document are light or dark. The scanner 13 scans the document one line at a time at a line extending across the document. This line is referred to as the scan line. The document to be copied is moved through the scan line at the same rate that the paper on which the printing is carried out by the printer 1] is moved through the print line and the optical scanner scans the document line by line at the scan line in synchronism with the printing of patterns of dots line by line on the paper by the printer at the print line. The scan line is divided into 12 segments which are scanned simultaneously. These 12 segments correspond to the 12 hammers 17. The output signals produced on the 12 output channels 31 represent the result of the simultaneous scanning of the twelve segments of the scan line. The output signals produced on output channels 31 are applied to AND gates 33 which also receive pulses from transducer 35 sensing a tone wheel 37 attached to the drum 15. As the drum l rotates, the tone wheel 37 will cause the transducer 35 to produce output pulses on channel 39, from which the pulses are applied to the AND gates 33. A pulse is produced on channel 39 each time the intersection of the helical bar 19 and the blades 21 pass through a dot print position. Dot print positions are positions along the print line at which the printer is designed to be capable of printing a dot. The spacing of the dot print positions is such that when dots are printed at two adjacent positions the dots will be contiguous.

Each of the AND gates 33 will be enabled when it receives a signal on the channel 31 connected thereto indicating that the document being copied at the corresponding segment of the scan line is dark. When an AND gate 33 is enabled, it will pass a pulse applied thereto from the transducer 35 on channel 39. Each pulse upon passing through one of the AND gates 33 will then pass through the corresponding OR gate 27 and be applied to the corresponding hammer firing circuit 29, whereupon the hammer firing circuit will apply a pulse to the corresponding hammer 17 and cause a dot to be printed. In this manner each hammer is controlled to print a pattern of dots corresponding to the dark areas of the document being copied at the corresponding segment of the scan line. When each line of the document is scanned and copied as described above, a facsimile of the document is produced.

The transducer 35, in addition to producing pulses corresponding to the times at which the intersection of the helical bar 19 with the hammer blades 17 pass through the dot print positions, also produces one output pulse for each revolution of the drum 15 on an output channel 41. Both outputs of the transducer 35 on channels 39 and 41 are applied to the optical scanner to maintain the optical scanner 13 in synchronism with the printer 11 as will be described below. In addition, both outputs of the transducer 35 are applied to the alphanumeric print control circuit 25 which are utilized by the alphanumeric print control circuit 25 to control the printing of dot patterns to form alphanumeric characters as described in the above-mentioned copending application Ser. No. 39,404.

The document scanned by the optical scanner is fed perpendicularly to the illustration of the scanner as shown in FIG. 2. The scanner as shown in FIGS. 2 and 3 comprises two L-shaped scanning bars 51 and 53 which are reciprocated alternately to scan across the document at the scan line by means of cams. Only one of the cams designated by the reference number 55 can be seen in FIG. 2. Twelve photoelectric scanning assemblies 57 are mounted on each L-shaped bar and are electrically connected by means of flexible cables 59 to the terminals on a fixed termal board 61. The output signals produced by the scanning assemblies are transmitted over the cables 59 to the output channels 31 of the optical scanner 13.

The document to be copied designated by the reference number 63 in FIG. 3 is driven by a belt and roller combination 65 under the L-shaped scanning bars 51 and 53. The belt and roller combination 65 comprises a belt 67 driven and guided by rollers 69. Rollers 71 pinch the document 63 against the belt 67 at the rollers 69 and the document is carried through the scan line directly under the scanning bars 51 and 53 by the belt 67. The document is carried on the belt 67 under a guiding plate 73 as it approaches the scan line. The plate 73 is provided with a slit 75 exposing the document 63 to the scanning bars 51 and 53 at the scan line. The slit 75 is covered by a transparent plate 77. Elongated lamps 79 positioned on each side of the scanning bars 51 and 53 illuminate the document at the scan line through the plate 77 and the aperture 75. Reflectors 80 increase the intensity of illumination from the lamps on the document at the scan line. As best shown in FIGS. 4, 5 and 6, each of the photoelectric scanning assemblies comprises a cylindrical channel 81 passing vertically through the vertically extending arm of the scanning bar. At the bottom of the cylindrical channel 81 is a lens 83 which focuses an image of the document at the scanning line on a photocell mounted on top of the scanning bar. The photocell is mounted in a housing 87, which as shown in FIG. 4, is fixed to the scanning bar by means of screws 89 passing through flanges in the housing 87 and screwed into the top surface of the scanning bar.

The mounting of the photocells in the housings 87 is illustrated in the sectional view through a housing 87 shown in FIG. 5, in which the photocell is designated by the reference number 90. The photocell 90 is lo cated at the bottom of a threaded opening extending through the top of the housing 87. The photocell fits into a recess defined at the bottom of this opening and is held in place by means of a screw 91, which is screwed into the threaded opening and presses down against an insulating washer 93, whichin turn holds the photocell 90 firmly in place. A channel 95 is defined through the screw 91 along the axis thereof and the electrical connection 97 to the photocell 90 passes through this channel surrounded by insulator 99. An aperture 101 is defined through the bottom of the housing 87 exposing the photocell to the channel 81. The lens 83 focuses portion of the document at the scan line on the photocell 90 through the aperture 101. The photocell 90 will only be sensitive to a small dot on the scan line at any given time because the bottom of the housing 87 masks the photocell 90 and only permits a small dot of the focused image of the document to pass through the aperture 101 to the photocell.

As shown in FIG. 6, the bottom of the channel 81 is enlarged to receive the lens 83, which is cemented in place at bottom of the channel 81. The wallsof the channel 81 are painted black to minimize reflection.

As the scanning bar is moved to scan the document 63, each of the photocells in each of the housings 87 is only responsive to a small dot at the scan line on the document 63, which dot will move across the document along the scan line. Each photocell will produce an output signal indicating continuously whether the document is light or dark at the focused dot as it moves across the scan line. As explained above with reference to FIG. 1, these signals are applied to the AND gates 33 which also receive pulses from the transducer 35. The gates 33 are each enabled to pass an applied pulse whenever the gate receives a signal from the corresponding photocell indicating that the document at the point on the scan line currently focused on the photocell is dark. As a result pulses will pass through the gates 33 to cause patterns of dots to be printed by the printer 11 in accordance with the signals received by the gates 33. In this manner the printer 11 is controlled to print a pattern of dots along the print line corresponding to the pattern of light and dark on the document along the scan line.

As best shown in FIG. 3, the two scanning bars 51 and 53 are canted at an angle so that the photoelectric scanning assemblies on bothscanning bars 51 and 53 focus on the same scan line. The bars are reciprocated alternately so that they scan the scan line alternately with one scanning bar scanning the scan line while the other scanning bar is being returned to the starting position from which it will scan the scanning line when the other scanning bar has completed its scan. The outputs of the photocells are connected to the output channels 31 through gates 33 which are enabled alternately in synchronism with the alternate scanning of the scan line by the scanning bars 51 and 53 so that only the signals from the photocells on the scanning bar, which is currently scanning in a forward direction, are passed to output channels 31.

The system for reciprocating the scanning bar 53 is illustrated in FIG. 7. A similar system is provided for reciprocating the scanning bar 51. As shown in FIG. 7, the scanning bar 53 is supported by rods 103 at one end and rods 107 at the other end. The rods are fixed to the arms of the L-shaped bar and ride in linear bearings 109 fixed to the frame (not shown). The ends of the rods 103 are connected by a cap 111, on which is mounted a cam follower 113, which is driven by a cam 115. The cam 115 is provided with an axially extending rim on the periphery thereof. This rim is engaged on both sides by rollers of the cam follower 113 so that the cam follower is positively driven in both directions by the cam 115. When the cam 115 is rotated, the cam follower 113 reciprocally drives the bar 53 along the scan line. The L-shaped bar 51 is driven by a similar manner by a similar cam so that it reciprocates alternately with the reciprocation of the bar 53.

When each of the scanning bars 51 and 53 is moved from its start position from left to right to carry out the scanning operation, it is moved at a constant speed by the cam so that the scanning of the document is carried out at a constant speed. The development of the two cam surfaces to achieve the constant speed operation is graphically illustrated in FIG. 8. In' FIG. 8 the displacement of each of the scanning bars is plotted against the angular position of the shaft driving the two cams which drive the two scanning bars 51 and 53. As shown in FIG. 8, one of the scanning bars is displaced moving from left to right at a constant speed between the angles 60 and 240 while the other scanning bar is displaced at a constant speed moving from left to right between the angles of 240 and 60. While one of the scanning bars is moving from left to right at a constant speed, the other scanning bar is returned to the start position from which the scanning is carried out. From the curve shown in FIG. 8, the cam surfaces can be derived. One of the cams is illustrated in FIG. 9. As shown in FIG. 9, the cam rotates in a counterclockwise direction and provides constant velocity to the cam follower moving it from left to right from the point designated 121 on the cam surface to the point designated 123.

The paper on which the printing is carried out by the printer 11 is moved continuously as the printing is carried out. If the hammer blades 21 were aligned exactly with the axis of the drum 15 perpendicular to the direction of paper travel, the printing by each blade would be slightly skewed on the paper instead of being perpendicular to the direction of paper travel. In the facsimile operation this would be perrnissable if the document is also moved continuously and the scanning is carried out directly perpendicular to the direction of movement of the document whereby the scanning with respect to the document would be slightly skewed corresponding to the skewed printing. However, because the printer 11 is also used to print alphanumeric characters, the skewing of the print lines defined by each of the blades 21 is not desirable as this would cause skewing of the alphanumeric characters printed. To prevent this skewing, the blades 21 are canted at slight angles so that the printing of the line of dots by each blade is directly perpendicular to the direction of paper travel. Accordingly, the optical scanner must scan the document in a similar manner or in other words scan the document at a slightly skewed angle instead of directly perpendicular to the direction of paper travel. Since the document is moving as the scanning proceeds, the

scanning with respect to the document will be directly perpendicular to the direction of movement by the document.

The photoelectric scanning assemblies on the bar 51 are aligned across the scan line directly perpendicular to the direction of paper feed. In addition, they must be spaced 1.1 inches apart to correspond to the hammer blade dimensions. To facilitate this alignment the photocell housings 87 are provided with oversized holes through which the screws 89 extend and clamp the housings to the bar. To achieve the desired alignment, a lamp is placed in each housing in place of the photocell. An image of the illuminated aperture 101 in each housing will then be focused on the'scan line. A chart of marks spaced precisely 1.1 inches apart along a straight line is positioned with the marks on the scan line and the position of each housing 87 is adjusted until the image of each aperture 101 falls on a mark on the chart. The housings 87 are then clamped in this precisely aligned position by the screws 89.

To achieve the skewed scanning, the rods 103 and 107 are canted slightly with respect to the long dimension of the bar. As shown in FIG. 7, the rods 103 are canted slightly in the direction from which the paper is fed and the rods 107 are canted slightly in the direction towards which the paper is fed. As a result, when the cam 115 reciprocates the bar 53, each transducer will scan in a direction slightly skewed with respect to normal to the direction of paper feed and as a result will scan on the document directly perpendicularlyv across the document with respect to the direction with which it is fed. Accordingly, the printer 11 with the canted blades 21 will accurately reproduce a facsimile of the document being scanned.

In order for the facsimile system to operate properly the reciprocation of the scanning bars 51 and 53 must be in synchronism with the rotation of the drum 15. For this reason the pulses produced by the transducer 35 are applied to the scanner 13. The pulses produced on channel 39 corresponding to the passing of the intersection of the helical bar and the hammer blades 21 through dot positions on the print line are applied to a frequency comparator 131. The pulses produced on channel 41 by the transducer 35 once for each revolu tion of the drum 15 are applied to a phase comparator 133. The motor which drives the two cams, which in turn drive the scanning bars 51 and 53, is designated in FIG. by the reference number 135. The motor 135 drives two tone wheels 137 and 139. The motor 135 should drive the cams 55 at a rotational speed of one half the speed at which the drum is driven since the two bars 51 and 53 will produce two scans of the scan line for each revolution of the cams. lf the motor 135 is driving the cams at the proper speed, that is at one half the speed at which the drum 15 is being driven, the tone wheel 137 will produce pulses in transducer 141 at the same frequency that the transducer 35 produces pulses on channel 39. The pulses produced by the transducer 141 are applied to the .frequency comparator 131, which compares the frequency of the pulses applied on channel 39 with the pulses produced by the transducer 141. If the frequency of the pulses produced by the transducer 141 is below the frequency of the pulses produced on channel 39, the frequency comparator 131 will produce an output signal applied to a motor speed control circuit 143 through summing resistor 145 signaling the motor control circuit to increase the speed of the motor 135 so that the motor '135 will increase its speed until the frequency of the pulses produced by the transducer 141 equals that of the pulses produced on channel 39. This portion of the circuit will get the motor 135 driving the cams 55 at exactly one half the speed at which the drum 15 is driven. In addition to being driven at the proper speed, the cams must have their angular position properly phased with respect to the angular position of the drum 15 so that the start of each scan by the optical scanner corresponds with the intersection of the helical bar 19 with the blades 21 being at the left side of each of the blades 21. To achieve this phase synchronism the tone wheel 139 is used. The tone wheel 139 produces two output pulses in a transducer 147 for each revolution of the cams 55. The tone wheel 139 is positioned on the output shaft of the motor 135 so that if the scanner 13 is in phase with the printer 11, the pulses produced in the transducer 147 will be simultaneous with the pulses produced by the transducer 35 on channel 41. The pulses produced by the transducer 147 are applied to phase comparator 133 which compares the time of the pulses with the timing of the pulses produced on channel 41. If the pulses produced by the transducer 147 occur a little after the pulses produced on channel 41, the phase comparator 133 will produce a signal calling for the motor control circuit 143 to speed the motor 135 up. If the pulses produced by the transducer 147 occur a little before the pulses produced on channel 41, the phase comparator will produce an output signal calling for the motor control circuit 143 to' slow the motor down. The output of the phase comparator 133 is applied through a low pass filter 149 and a summing resistor 151 to the motor control circuit 143. Thus, the motor control circuit 143 will respond to the output of the phase comparator 133 to increase or decrease the speed of the motor 135 until the pulses produced by the transducer 147 occur simultaneously with those produced on channel 41 and the scanner 13 will be in exact synchronism with the drum 15.

The phase comparator, for example, may comprise a pair of bistable flipflops one responding to the output pulses produced by the transducer 147 and the other responding to the pulses produced on channel 41. Thus one of the flipflops produces a square wave in synchronism with the pulses on channel 41 and the other flipflop will produce a square wave in synchronism with the pulses produced on channel 147. The two square waves can be summed in opposition with one square wave being positive going and the other square wave being negative going. If the pulses occur simultaneously, the two square waves will cancel each other out. If the pulses do not occur simultaneously the summation will produce an alternating output which will have a phase relative to the square waves depending upon whether the scanner is lagging or leading the printer. This alternating output can be converted to an error signal having a polarity indicating whether the motor is to be speeded up or slowed down. The low pass filter 149 will smooth out the error signal into a continuous signal calling for motor speed up or motor slow down to achieve the proper phase.

FIG. 11 shows an alternative embodiment of the facsimile system in which the hammers are so actuated that they strike with a force proportional to the darkness of the region scanned. In this embodiment, a nonlinear amplifier couples each of the output lines 31 to a respective hammer firing circuit 23. The amplifier alphanumeric data. The above description is of a preferred embodiment of the invention and many modifications may be made thereto without departing from the spirit and scope of the invention.

I claim:

l. A facsimile system comprising dot printing means operable to print patterns of dots along different segments of a print line simultaneously, scanning means to scan a document to be copied along different segments of a scan line simultaneously to produce output signals representing the patterns of said document at said segments of said scan line, and means responsive to the output signals of said scanning means to control said printing means to print dots in patterns along said segments of said print line simultaneously corresponding to the patterns of said document along said segments of said scan line, said scanning means comprising a scanning bar, a plurality of photocells mounted on said scanning bar, focusing means mounted on said scanning bar to focus a dot in each segment of said scan line on a different one of said photocells, and means to reciprocate said bar to cause the position of the dots focused on said photocells to move along the segments of said scan line.

2. A facsimile system as recited in claim 1 wherein said scanning means further comprises a second scanning bar, a second plurality of photocells mounted on said second scanning bar, second focusing means mounted on said second scanning bar to focus a dot in each segment of said scan line on a different one of said photocells of said second plurality, and means to reciprocate said second scanning bar alternately with the reciprocation of said first scanning bar to cause the position of the dots focused on the photocells of said second plurality to move along the segments of said scan line.

3. A facsimile system comprising dot printing means operable to print patterns of dots along different segments of a print line simultaneously, scanning means to scan a document to be copied along different segments of a scan line simultaneously to produce output signals representing the patterns of said document at said segments of said scan line, and means responsive to the output signals of said scanning means to control said printing means to print dots in patterns along said segments of said print line simultaneously corresponding to the patterns of said document along said segments of said scan line, said printing means including means to move the medium on which said printing is carried out continuously through said print line, and said scanning means including means to move the document to be copied continuously through said scan line, said segments of said print line being skewed relative to perpendicular to the direction in which said medium is moved through said print line whereby said printing means prints dots on said medium in lines extending perpendicularly to the direction of travel of said medium, said segments of said scan line being skewed relative to the direction of movement of said document through said scan line whereby said scanning means scans said document relative to said document perpendicular to the direction of motion of said document.

4. A facsimile system as recited in claim 3 further comprising means to control said dot printing means to print dots in patterns of selected alphanumeric characters.

5. An optical scanner for scanning a document along a scan line comprising a first scanning bar and a second scanning bar, a first photoelectric cell mounted on said first scanning bar and a second photoelectric cell mounted on said second scanning bar, first focusing means mounted on said first scanning bar for focusing a first dot in said scan line on said first photocell, second focusing means mounted on said second scanning bar for focusing a second dot in said scan line on said second photocell, and means to reciprocate said scanning bars alternately to cause said first and second dots to move forward along said scan line alternately.

6. An optical scanner as recited in claim 5 wherein said scan line is divided into a plurality of segments, and wherein a plurality of photocells is mounted on each of said scanning bars, and a plurality of focusing means are mounted on each of said scanning bars to focus a dot from each of said segments on a different photocell mounted on each of said scanning bars. 

1. A facsimile system comprising dot printing means operable to print patterns of dots along different segments of a print line simultaneously, scanning means to scan a document to be copied along different segments of a scan line simultaneously to produce output signals representing the patterns of said document at said segments of said scan line, and means responsive to the output signals of said scanning means to control said printing means to print dots in patterns along said segments of said print line simultaneously corresponding to the patterns of said document along said segments of said scan line, said scanning means comprising a scanning bar, a plurality of photocells mounted on said scanning bar, focusing means mounted on said scanning bar to focus a dot in each segment of said scan line on a different one of said photocells, and means to reciprocate said bar to cause the position of the dots focused on said photocells to move along the segments of said scan line.
 2. A facsimile system as recited in claim 1 wherein said scanning means further comprises a second scanning bar, a second plurality of photocells mounted on said second scanning bar, second focusing means mounted on said second scanning bar to focus a dot in each segment of said scan line on a different one of said photocells of said second plurality, and means to reciprocate said second scanning bar alternately with the reciprocation of said first scanning bar to cause the position of the dots focused on the photocells of said second plurality to move along the segments of said scan line.
 3. A facsimile system comprising dot printing means operable to print patterns of dots along different segments of a print line simultaneously, scanning means to scan a document to be copied along different segments of a scan line simultaneously to produce output signals representing the patterns of said document at said segments of said scan line, and means responsive to the output signals of said scanning means to control said printing means to print dots in patterns along said segments of said print line simultaneously corresponding to the patterns of said document along said segments of said scan line, said printing means including means to move the medium on which said printing is carried out continuously through said print line, and said scanning means including means to move the document to be copied continuously through said scan line, said segments of said print line being skewed relative to perpendicular to the direction in which said medium is moved through said print line whereby said printing means prints dots on said medium in lines extending perpendicularly to the direction of travel of said medium, said segments of said scan line being skewed relative to the direction of movement of said document through said scan line whereby said scanning means scans said document relative to said document perpendicular to the direction of motion of said document.
 4. A facsimile system as recited in claim 3 further comprising means to control said dot printing means to print dots in patterns of selected alphanumeric characters.
 5. An optical scanner for scanning a document along a scan line comprising a first scanning bar and a second scanning bar, a first photoelectric cell mounted on said first scanning bar and a second photoelectric cell mounted on said second scanning bar, first focusing means mounted on said first scanning bar for focusing a first dot in said scan line on said first photocell, second focusing means mounted on said second scanning bar for focusing a second dot in said scan line on said second photocell, and means to reciprocate said scanning bars alternately to cause said first and second dots to move forward along said scan line alternately.
 6. An optical scanner as recited in claim 5 wherein said scan line is divided into a plurality of segments, and wherein a plurality of photocells is mounted on each of said scanning bars, and a plurality of focusing means are mounted on each of said scanning bars to focus a dot from each of said segments on a different photocell mounted on each of said scanning bars. 